The invention relates to a master disk for a magnetic recording medium.
After magnetic disks (also called “hard disks”) used in the hard disk drives which have been rapidly widespread in recent years are delivered to disk drive manufacturers from magnetic disk manufacturers, before installation in disk drives, format information and address information are generally written onto the magnetic disks. This writing can be performed using magnetic heads. However, a method of batch transfer from a master disk on which such format information and address information have been written is more efficient, and is preferred.
As the batch transfer (magnetic printing) methods, generally, a magnetic transfer method employing magnetic properties is popular. In the magnetic transfer method, the master disk and a slave disk which is the transfer target disk are arranged to closely contact with each other, and an electromagnet device, permanent magnet device, or other magnetic field generating means is arranged on one side or on both sides to apply a magnetic field, so that a magnetization pattern corresponding to the servo signals and other information on the master disk is transferred all at once. In the magnetic transfer method, recording can be performed suitably without changing the relative positions of the master disk and slave disk. Moreover, there is an advantage that the time required for recording is extremely short. In particular, through recent progress in ultra-fine patterning technology, such as electron beam lithography techniques, signal patterning with minimum bit length of 100 nm or less has become possible, and batch writing of signals equivalent to the areal densities of current hard disk can now be performed using magnetic transfer.
In the past, various proposals of such magnetic transfer methods have been made. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 10-40544: Patent Document 1, batch transfer is performed from a master disk on which a relief pattern comprising magnetic material is formed, corresponding to information written onto the surface of the substrate. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 10-269566: Patent Document 2, closeness between the master disk and slave disk during magnetic transfer is improved. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2005-228462: Patent Document 3, by using laser light in irradiation through a master information carrier, where a pattern in shapes corresponding to servo signals or similar is formed on a translucent nonmagnetic substrate by arranging opaque ferromagnetic thin film, the coercivity is lowered in the portions irradiated with the laser light so as to perform magnetic transfer of servo signals or similar.
Here, a magnetic transfer method of the conventional art is explained, referring to FIGS. 1A-1C. FIG. 1B is a sectional view taken along a line 1B-1B in FIG. 1A. During magnetic transfer, a master disk 10 and a slave disk 30 are set as shown in FIG. 1C, the slave face 3 of the slave disk 30 is brought into contact with the protruding portions 2 formed by soft magnetic material on the master disk 10, and a prescribed pressing force is used to closely contact them each other.
Then, in the state in which the master disk 10 and slave disk 30 are in close contact, magnetic field generating means (not shown) is used to apply a magnetic field 5 in the direction shown in the figure, to perform batch transfer of the relief pattern of the master disk 10 onto the slave face 3 of the slave disk 30. Magnetic transfer by the master disk 10 may be performed to one face by bringing one face of the slave disk 30 into close contact with the master disk 10, or may be performed simultaneously to both faces, with a pair of master disks (not shown) brought into close contact with both faces of the slave disk 30. At the time of application of the magnetic field, the master disk 10 and slave disk 30 are integrally rotated. In addition to this method, the magnetic field generation means may be moved in rotation.
Next, a method for manufacturing a master disk of the conventional art is explained, referring to FIGS. 2A-2D. First, as shown in FIG. 2A, sputtering or another method is used to deposit soft magnetic material 2′ (CoFe and the like) on a substrate 1 (silicon, glass, quartz, and the like) with a flat and clean surface. Then, an electron beam resist liquid is applied to form a resist film 7 by spin-coating. Then, using an electron beam exposure device (not shown) provided with a high-precision rotating stage or X-Y stage, the substrate 1 mounted on this stage is irradiated by an electron beam which is modulated corresponding to servo signals or other information, exposing the resist film 7 to the desired relief pattern. Then, development processing is performed to obtain the structure shown in FIG. 2B. Next, as shown in FIG. 2C, the patterned resist film 7 is used as a mask to perform RIE dry etching of the soft magnetic layer 2′ using reactive gas and the like, or Ar gas is used to perform ion milling, or similar processing is performed to form protrusions 2 formed of the soft magnetic material. Finally, as shown in FIG. 2D, the resist film 7 is removed using oxygen plasma, resist stripping liquid, and the like. Through these processes, a master disk 10 can be manufactured in which protrusions 2 of soft magnetic material are formed, said protrusions 2 being arranged in a pattern corresponding to servo signals or other information.
However, in the technology disclosed in Patent Documents 1 and 2, the soft magnetic material used in protruding portions of the master disk is required to have a high saturation magnetic flux density, high permeability, low coercivity, and the like. Moreover, the shape should be rectangular as much as possible, and it is preferred that the thickness be of approximately the same dimension as the size of a bit. Hence, if material capable of meeting these requirements is selected, and if there is no technique for forming this material into fine shapes, a master disk with high transfer performance cannot be manufactured. Also, in order to further improve the contact of the master disk and slave disk (corresponding to the magnetic recording medium) and further improve transfer performance, if methods such as applying pressure for close contact within a chamber structure as well as reducing the pressure, and the like are used, there is a problem that the magnetic field necessary to magnetize the slave disk must pass through the chamber, so that the distance is increased, and magnets capable of generating very strong magnetic fields become necessary.
In the technology disclosed in Patent Document 3, when manufacturing a master disk, just as in the conventional art, there is the preeminent problem that ferromagnetic material optimized for magnetic transfer must be selected and processed.
The invention has been made in light of the above problems, and has a first object to provide a master disk, which can be manufactured more easily than the conventional art, and which realizes easy batch transfer compared with the magnetic transfer.
A second object of the invention is to provide a method for manufacturing a magnetic recording medium using the master disk of this invention.
Further objects and advantages of the invention will be apparent from the following description of the invention.